This invention relates to motor controls, and more particularly to a power factor controller which provides input power to a motor commensurate with the loading on the motor.
An AC induction motor is one that is commonly utilized for numerous appliances and machinery. It generally runs at a constant speed which is independent of both load and applied voltage. However, it is an inefficient motor in that it cannot adjust the amount of current it draws in proportion to its loading. Thus, whether the motor is loaded or unloaded, essentially the same current is drawn so that the motor efficiency goes down when the load decreases.
In order to improve the situation, there has been provided a power factor control system for AC induction motors described in U.S. Pat. No. 4,052,648. This system samples line voltage and current through the motor and decreases power input to the motor proportional to the detected phase displacement between the current and voltage to thereby provide less power to the motor, as it is less loaded.
While the aforementioned power factor control system has provided improved efficiency to an AC induction motor, it does not provide any indication of such efficiency and accordingly the user is unaware of whether the system is effective in providing improvement. In many cases the user can vary the load on the motor in order to optimize the improvement. However, being unaware of the improvement being provided by the control system he cannot adjust the load accordingly.
An additional difficulty with the aforementioned circuit occurs in connection with starting up the motor. Since the motor is controlled only through the control system, when the motor is initially started, it is necessary to simultaneously commence operation of the power factor control system. Accordingly, the motor will only receive power as directed by the control system. As a result, when the motor is initially energized, the power factor control system will delay the ability of the motor to reach full speed.
Additional difficulties with the aforementioned control circuit concern the necessity for numerous components including various amplifiers, and other parts which increase the cost of the control system, as well as the complexity thereof.
Accordingly, there is need for improving the aforementioned power factor control system in order to eliminate these and other problems and provide an improved power factor controller.